In the automotive industry, remote keyless entry ("RKE") systems have become standard equipment on many new vehicles. Comprising a receiver within the car and a number of fob transmitters for transmitting a message to the receiver, RKE systems enable users to control several vehicle functions remotely, such as the door locks and trunk, for example.
In providing remote control to vehicle functions, a problem arises as to restricting remote access to the automobile's owners and other authorized users. To prevent unauthorized access, an identification system is incorporated with a security code or codes within both the fob transmitter and receiver. The receiver receives a transmitted signal having a command and an identification or security code and compares the received code with the security code stored in its memory. If the receiver determines the received security code to match the stored code, the command is initiated for execution.
As the demand for RKE systems has evolved in the marketplace, greater emphasis has been placed on increased security, reliability and flexibility. With the development of sophisticated electronics, presently, a transmitted message may be decoded and retransmitted at a later time. This is in part because in these known systems the transmitted message does not change between transmissions.
One area of focus has been the incorporation of encryption techniques into RKE system to decrease the likelihood of unauthorized reception and retransmission of the originally transmitted signal comprising both a command and a security code. Security by encryption may be accomplished using an algorithm in the transmitter for manipulating data into random or "rolling" codes. As a result of such an encryption algorithm, each code transmitted will be different from the last, making it difficult for the code to be copied and the vehicle security defeated.
However, in utilizing an encryption scheme, it is also necessary that the transmitter and receiver remain in synchronization with each other. If the transmitter and receiver are asynchronized, the transmitted command residing within an encrypted message will not be initiated by the receiver. A resultant rolling code, as calculated by the receiver and transmitter utilizing such an encryption scheme, must be equivalent to initiate a received command.
The issue of synchronization is of particular relevance in certain circumstances. First, if a user inadvertently enables the transmission of a rolling code encrypted command while the transmitter is out of range, the transmitter will be at least one encryption step ahead of the receiver. Further, should either transmitter or receiver suffer a power loss, the unaffected component will be at least one encryption step ahead of the receiver. Moreover, the system may be asynchronized if the user uses an alternate transmitter. This situation arises in the event several transmitters are supplied with a single receiver or if one transmitter is damaged and a replacement transmitter is supplied.
Therefore, there is a demand for a method and system for resynchronizing a transmitter that is asynchronized with a receiver generally. Moreover, a need further exists for an RKE system having utilizing such a method and system for resynchronizing an asynchronized RKE transmitter with an RKE receiver.